In automobile industry, electrical industry, machine industry, and the like, there is a growing demand for an acceleration sensor (or accelerometer) which can accurately detect an acceleration and an angular velocity. Especially, a small acceleration sensor which can detect the acceleration for each two-dimensional or three-dimensional component is desired.
In order to meet the above demand, there has been proposed an acceleration sensor which has a proof mass having a movable structure and formed on a semiconductor substrate such as a silicon substrate and converts a mechanical distortion, generated in a substrate based on the acceleration applied to the proof mass, into an electrical signal by a sensor based on various conversion principles. As the acceleration sensor, there have been known a sensor utilizing a piezoresistive effect, a sensor utilizing a change of a capacitance, a sensor utilizing a piezoelectric bimorph effect, a sensor utilizing a frequency change of a piezoelectric bending resonator, and the like.
However, the piezoresistive effect has a large temperature dependency, and in order to perform accurate measurement, temperature compensation should be performed. The sensor utilizing a change of a capacitance has an advantage that the manufacturing cost is low. However, since the amount of the formed capacitance is small, it is disadvantageous in that signal processing is difficult. In the sensor utilizing a piezoelectric bimorph effect, it is difficult to detect a static acceleration, and there is a problem that the range of utilization is limited.
The sensor utilizing a frequency change of a piezoelectric bending resonator is known. Namely, the sensor has a constitution that two beam-shaped vibrating arm portions are arranged in a planar manner through a through-hole, and the ends of the two vibrating arm portions are fixed. The vibrating arm portions vibrate in a direction parallel to the plane.
This type of sensor has such characteristics that it has a small temperature-dependency and a high detection sensitivity and can detect the static acceleration. For example, a sensor using a quartz crystal as a material of the piezoelectric bending resonator is proposed; however, there is such a drawback that the size reduction is difficult in manufacturing.